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From: allanh@netcom.COM (Allan N. Hessenflow)
Newsgroups: comp.dsp
Subject: Re: factoring matrices question
Summary: solved
Message-ID: <1991Apr10.051439.1493@netcom.COM>
Date: 10 Apr 91 05:14:39 GMT
References: <1991Apr8.200939.5533@netcom.COM>
Organization: Netcom - Online Communication Services  UNIX System {408 241-9760 guest}
Lines: 24

In article <1991Apr8.200939.5533@netcom.COM>, I write:
> I've been told that there's a way to factor the following matrix so that,
> when it's multiplied by a column vector, the total number of multiplications
> are reduced (2:1?) at the expense of some additions.  However, I can't see
> how.  Any insights would be appreciated.
> 
>  c3 -c5  c1 -c7
>  c5  c3 -c7 -c1
> -c7  c1  c3  c5
>  c1  c7 -c5  c3
> 
> where cn=cos(n*pi/16).

Everyone can stop thinking about this; I've figured it out (after receiving
three replies to my posting, all of which say it's clearly impossible!).

In case you're curious, I can't reduce the multiplies 2:1, but I can reduce
it to 10 from the original 16.

allan


-- 
Allan N. Hessenflow   {apple|claris}!netcom!allanh    allanh@netcom.com